The present invention relates to subterranean cementing operations and associated methods, and more particularly, to foamed cement compositions that comprise an additive, the additive comprising an anionic foam stabilizer and at least one of an anionic foaming agent or a Zwitterionic foam booster.
Hydraulic cement compositions commonly are utilized in subterranean operations, particularly subterranean well completion and remedial operations. For example, hydraulic cement compositions may be used in primary cementing operations, whereby pipe strings such as casings and liners are cemented in well bores. In performing primary cementing, hydraulic cement compositions may be pumped into an annular space between the walls of a well bore and the exterior surface of a pipe string disposed therein. The cement composition is permitted to set in the annular space, thereby forming an annular sheath of hardened substantially impermeable cement therein that substantially supports and positions the pipe string in the well bore, and that bonds the exterior surface of the pipe string to the walls of the well bore. Hydraulic cement compositions also are used in remedial cementing operations that involve plugging highly permeable zones or fractures in well bores, plugging cracks and holes in pipe strings, and the like.
Cement compositions utilized in subterranean operations may be lightweight to prevent excessive hydrostatic pressure from being exerted on subterranean formations penetrated by the well bore, whereby the formations may be unintentionally fractured. One type of lightweight cement composition is a foamed cement composition, i.e., a cement composition that comprises a gas. In addition to being lightweight, the gas contained in the foamed cement composition improves the ability of the composition to maintain pressure and prevent the flow of formation fluids into and through the cement composition during its transition time, i.e., the time during which the cement composition changes from a true fluid to a set mass. Foamed cement compositions are also advantageous because they have low fluid loss properties and may act to prevent the loss of fluid circulation. Additionally, foamed cement compositions when set have a lower modulus of elasticity than non-foamed cements, which is often desirable as it enables the resultant set cement, inter alia, to resist hoop stresses exerted on the set cement in the annulus.
A foamed cement composition generally may be prepared by mixing a gas, such as air or nitrogen, with the cement composition. Foamed cement composition typically further may comprise a variety of surfactants commonly referred to as “foaming agents” for facilitating the foaming of a cement composition and various other surfactants commonly referred to as “foam stabilizers” for preventing the components of the foamed cement composition from prematurely separating. While a variety of foaming agents and foam stabilizers are well known in the art, problems have been associated with their use. For example, certain foaming agents, such as those consisting of a surfactant of Formula 1, R—OR′)n—OSO3—X+, and foam stabilizers, such as a glycol of Formula 2, CH3—(CH2CH2O)nH, or a betaine surfactant, may lower the compressive strength of the resultant set cement composition. Furthermore, upon mixing, the foaming agents and foam stabilizers used heretofore with water, gelation may occur, which is undesirable. Moreover, some foaming agents and/or foam stabilizers may have undesirable environmental characteristics and/or may be limited by strict environmental regulations in certain areas of the world.